Don’t worry about it; most older houses will have woodworm somewhere or other. Take up the offer to get it treated and be grateful this isn’t the USA or somewhere hot where all kinds of things can eat your house. Even if the treatment failed, woodworm progresses slowly especially in a cool place like the roof; you will find the roof beams in old barns have been eaten to hell by worm and are still doing the job.
Be much more concerned about dry rot, which is much more serious and difficult to eradicate. This is a worry in older houses with poorly ventilated spaces under the floors or leaking roofs.